Re: TC Inductance Formulas...


>I've been using Wheeler's with a slight modification for helical 
>coils. Instead of a bottom line = 9r + 10h,  I've been using a
>bottom line = 10(r + h). It seems slightly better for typical
>Tesla secondaries. In any case, Wheeler seems to come within about
>5% worst case and often better in my experience.

Sorry for getting this out so late but my outgoing mail has been down...

I personally like the most exact inductance calculation I can get, but my
problem is that out of 7 different formulas I have used to calculate the
inductance of the secondary, only six are even near close to one another
(one is completely off at about 23mH while the others range from 26mH to
29mH).  Here is what I have calculated using the different formulas (i1) - (i7):

For a 6" TC...w/out discharge toroid

Inductance Calculations

                          (H)           (mH)         (uH)
L:             (i1)   0.026275632  26.275631704  26275.631704
               (i2)   0.026275632  26.275631704  26275.631704
               (i3)   0.029201946  29.201945986  29201.945986
               (i4)   0.026295601  26.295601184  26295.601184
               (i6)   0.029193514  29.193514397  29193.514397
               (i7)   0.029193514  29.193514397  29193.514397

L:(Average)    (SUM)  0.166435839  166.43583937  166435.83937
               (AVG)  0.027739307  27.739306562  27739.306562

The above is the inductance calculated using only the diameter of the coil
from itself, nothing else is taken into acount.

L[m]:          (i1)   0.026507712  26.507711770  26507.711770
               (i2)   0.026507712  26.507711770  26507.711770
               (i3)   0.029473178  29.473177587  29473.177587
               (i4)   0.026527858  26.527857631  26527.857631
               (i6)   0.029464668  29.464667684  29464.667684
               (i7)   0.029464668  29.464667684  29464.667684

L[m]:(Average) (SUM)  0.167945794  167.94579413  167945.79413
               (AVG)  0.027990966  27.990965688  27990.965688
The above L[m] is calculated using the mean radius or mean diameter, that
being the radius measured from the center of the coil form to center of
conductor in the winding.

L[p]:          (i1)   0.026296048  26.296047897  26296.047897
               (i2)   0.026296048  26.296047897  26296.047897
               (i3)   0.029225799  29.225799111  29225.799111
               (i4)   0.026316033  26.316032893  26316.032893
               (i6)   0.029217361  29.217360635  29217.360635
               (i7)   0.029217361  29.217360635  29217.360635
L[p]:(Average) (SUM)  0.166568649  166.56864907  166568.64907
               (AVG)  0.027761442  27.761441511  27761.441511

The above L[p] is a "prime" calculation, I am trying to determine which
method is closest to the actual measured inductance of the coil.  The
"prime" measurement is taken from the inner side of the conductor, thus it
accounts for the coil form diameter plus the build or thickness of the
insulator/polymer on the magnet wire, in this particular case it was
calculated using double build #22AWG Heavy Armored Poly-Thermaleze (BELDEN).
The first insulator coat is Cross-Linked Modified Polyester (8.167e-4 in
thick) and the second insulator coat is an Amide-Imide Polymer (4.083e-4 in
thick).  In total with the conductor and the insulation build the magnet
wire has a diameter of 2.78e-2in.

Sorry if the above calculations seem alittle weird or eccentric, but I am a
scientist and I generally quest for perfection in my work.

Note how the ranges vary, and actually the average of the "prime"
calculation is the closest to the inductance I have calculated by using the
measured resonace frequency.  I myself didn't actually measure the resonant
frequency, I had a ECE graduate student at the university do it, I beleive
he used a signal generator and a scope,as well as a resistance, all in
series with the inductor, at least I think that is what he said.  Anyway he
said he had and could do it so I let him.  If this measured resonance is in
error please let me know, power and propulsion physics is my forte, not
electrical engineering so to speak.

Any suggestions or comments...


| Timothy A. Chandler                ||   M.S.Physics/B.S.Chmeistry     |
| NASA-Langley Research Center       ||   George Mason University       |
| Department of Energy               ||   Department of Physics         |
| FRT/Alpha - NASALaRC/DOE JRD/OPM   ||   Department of Chemistry       |
| CHOCT FR Designation #82749156/MG09||   OPC-EFC                       |
|                 Private Email Address:  tchand-at-slip-dot-net               |